1. Field of the Invention
The present invention relates to a variable resistance circuit that has a variable resistance value being gradually variable, an operational amplification circuit employing this variable resistance circuit, and a semiconductor integrated circuit employing this operational amplification circuit.
2. Description of the Background Art
In recent years, optical disk drives such as a CD (compact disk) drive, a CD-ROM (compact disk read only memory) drive and the like come into wide use, followed by development of various semiconductor integrated circuits applied to these optical disk drives.
FIG. 7 is a block diagram showing the structure of a conventional semiconductor integrated circuit applied to a CD-ROM drive.
The circuit shown in FIG. 7, formed by a plurality of semiconductor integrated circuits, comprises a signal processing circuit 200, an RF (radio frequency) amplifier 220, a drive circuit 230, a microcomputer 240 and a DRAM (dynamic random access memory) 250.
The signal processing circuit 200 includes a DSP (digital signal processor) 201, a DAC (digital-to-analog converter) 202, a servo circuit 203 and an error correction circuit 204. The RF amplifier 220 is formed by a bipolar integrated circuit with different components, and the signal processing circuit 200 is integrated into a single chip by a CMOS (complementary metal oxide semiconductor) integrated circuit.
An optical pickup 210 converts data recorded on a CD-ROM disk to an RF signal, and outputs the RF signal to the RF amplifier 220. The RF amplifier 220 generates a reproduced signal (EFM (eight to fourteen modulation) signal), a focus error signal and a tracking error signal etc., and outputs these signals to the signal processing circuit 200.
The signal processing circuit 200 creates a control signal for controlling the optical pickup 210 from the focus error signal, the tracking error signal etc. through the DSP 201 and the servo circuit 203, and outputs the control signal to the drive circuit 230. The drive circuit 230 drives an actuator provided in the optical pickup 210 in response to the input control signal, for controlling the optical pickup 210 to reproduce an excellent RF signal.
The signal processing circuit 200 further performs error correction of the reproduced data by the error correction circuit 204 with the DRAM 250, for converting the reproduced data to an analog signal by the DAC 202 and outputting the analog signal when reproducing a sound signal.
The microcomputer 240 serves as a system controller controlling operations of the overall drive and transmits/receives data etc. to/from the signal processing circuit 200 at need so that the CD-ROM drive executes various operations.
The RF amplifier 220 of the CD-ROM drive having the aforementioned structure internally varies the amplification factor for the RF signal with various levels of RF signals for reproducing data from various optical disks such as a CD, a CD-ROM, a CD-RW (compact disk rewritable) and the like. Therefore, the RF amplifier 220 comprises a PGA (programmable gain amplifier) or the like varying the amplification factor for the RF signal, and employs a variable resistance circuit settable to various resistance values for gain control.
FIG. 8 is a circuit diagram showing the structure of a conventional variable resistance circuit. The variable resistance circuit shown in FIG. 8 includes a decoding circuit 300, switches SW0 to SW255 and resistors TR0 to TR255.
The 256 resistors TR0 to TR255 are serially connected with each other, the resistance values of all resistors TR0 to TR255 are set to R (xcexa9), and the resistors TR0 to TR255 are identical to each other. The switches SW0 to SW255, connected in parallel with the corresponding ones of the resistors TR0 to TR255 respectively, are identical to each other. When the switches SW0 to SW255 are turned on, the resistors TR0 to TR255 connected therewith are so bypassed as to change the resistance value of the variable resistance circuit.
Control signals d1 to d8 of eight bits are input in the decoding circuit 300. The control signal d1 expresses the least significant bit, the control signal d8 expresses the most significant bit, and the respective values of 0 to 255 can be expressed by the control signals d1 to d8. The decoding circuit 300 decodes the control signals d1 to d8 of eight bits and outputs control signals for turning on/off the switches SW0 to SW255 and setting resistance values corresponding to data expressed by the control signals d1 to d8 of eight bits to the switches SW0 to SW255.
The switches SW0 to SW255 are turned on/off by the control signals output from the decoding circuit 300 respectively, and the ON-state switches bypass the resistors. Therefore, the resistance value of the variable resistance circuit is set to an arbitrary value among O (xcexa9), R (xcexa9), 2R (xcexa9), . . . , 255R (xcexa9) by bypassing an arbitrary resistor among the 256 resistors TR0 to TR255 in response to the control signals d1 to d8 of eight bits.
FIG. 9 is a circuit diagram showing the structure of another conventional variable resistance circuit. The variable resistance circuit shown in FIG. 9 includes switches SW10 to SW17 and resistors TR10 to TR17. The eight resistors TR10 to TR17 are serially connected with each other. The resistors TR10, TR11 and TR12 have resistance values R (xcexa9), 2R (xcexa9) and 4R (xcexa9) respectively, and the resistance values of the subsequent resistors TR13 to TR17 are successively doubled so that the resistance value of the final resistor TR17 is set to 128 R (xcexa9).
The switches SW10 to SW17 are connected in parallel with the corresponding ones of the resistors TR10 to TR17 respectively, and turned on/off thereby bypassing the resistors TR10 to TR17 connected therewith.
The aforementioned control signals d1 to d8 of eight bits are input in the switches SW10 to SW17 respectively, for setting the resistance value of the variable resistance circuit to an arbitrary value among O (xcexa9), 2R (xcexa9), . . . , 255R (xcexa9).
Linearity of the resistance value of the variable resistance circuit shown in FIG. 9 is deteriorated due to parasitic resistances of the switches SW10 to SW17. Assuming that the parasitic resistance value of each of the switches SW10 to SW17 is r (xcexa9), the resistance value of the variable resistance circuit is 255R (xcexa9) when all switches SW0 to SW17 are off, 254R+rxc3x97R/(r+R) (xcexa9) when the switch SW10 is on and the switches SW11 to SW17 are off, 253R+2rxc3x97R/(r+2R) (xcexa9) when the switch SW11 is on and the switches SW10 and SW12 to SW17 are off, or 252R+rxc3x97R/(r+R)+2rxc3x97R/(r+2R) (xcexa9) when the switches SW10 and SW11 are on and the switches SW12 to SW17 are off.
Thus, the change rate of the resistance value of the variable resistance circuit is Rxe2x88x92rxc3x97R/(r+R) (xcexa9), R+rxc3x97R/(r+R)xe2x88x922rxc3x97R/(r+2R) (xcexa9) or Rxe2x88x92rxc3x97R/(r+R) (xcexa9). In other words, even if the change rate of the resistance value by the resistors TR10 to TR17 is constant, the change rate of the resistance value by the parasitic resistances of the switches SW10 to SW17 is not constant. Therefore, the change rate is not constant but the linearity of the resistance value of the variable resistance circuit is deteriorated due to the parasitic resistances of the switches SW10 to SW17.
An object of the present invention is to provide a variable resistance circuit capable of setting the resistance value in high precision, an operational amplification circuit employing this variable resistance circuit and a semiconductor integrated circuit employing this operational amplification circuit.
A variable resistance circuit that has a variable resistance value being gradually variable, according to one aspect of the present invention, comprises a resistance circuit including a plurality of resistors serially connected and a bypass circuit connected in parallel with the resistance circuit for bypassing one or more resistors selected from the plurality of resistors, wherein the bypass circuit includes a plurality of transistors selectively turned on or off, the variable resistance value is determined by a combined resistance value of a parasitic resistance of one or more transistors being turned on and one or more resistors being bypassed as well as a combined resistance value of one or more resistors being not bypassed, and gate widths of the plurality of transistors are so set that the variable resistance value varies approximately in steps of a predetermined value.
In the variabe resistance circuit, the variable resistance value is determined by a combined resistance value of a parasitic resistance of one or more transistors being turned on and one or more resistors being bypassed as well as a combined resistance value of one or more resistors being not bypassed. Thus, various resistance values can be set by selectively turning on or off the plurality of transistors. The gate widths of the plurality of transistors are so set that the variable resistance value varies approximately in steps of a predetermined value. Thus, linearity of the variable resistance value can be ensured. Consequently, the resistance value can be set in high precision.
The plurality of transistors may be connected to ends of the plurality of resistors respectively.
A variable resistance circuit that has a variable resistance value being gradually variable, according to another aspect of the present invention, comprises a resistance circuit including a plurality of resistors serially connected; and a switch circuit connected in parallel with the resistance circuit for bypassing one or more resistors selected from the plurality of resistors, wherein the switch circuit includes a plurality of switches selectively turned on or off, the variable resistance value is determined by a combined resistance value of a parasitic resistance of one or more switches being turned on and one ore more resistors being bypassed as well as a combined resistance value of one or more resistors being not bypassed, and parasitic resistance values of the plurality of switches in an ON state are so set that the variable resistance value varies approximately in steps of a predetermined value.
In the variabe resistance circuit, the variable resistance value is determined by a combined resistance value of a parasitic resistance of one or more switches being turned on and one or more resistors being bypassed as well as a combined resistance value of one or more resistors being not bypassed. Thus, various resistance values can be set by selectively turning on or off the plurality of switches. The parasitic resistance values of the plurality of switches in an ON state are so set that the variable resistance value varies approximately in steps of a predetermined value. Thus, linearity of the variable resistance value can be ensured. Consequently, the resistance value can be set in high precision.
The plurality of switches may include a plurality of transistors connected to ends of the plurality of resistors respectively. Each of the plurality of switches may include a CMOS switch. In this case, a circuit including the variable resistance circuit can be formed by a CMOS integrated circuit.
A variable resistance circuit that has a variable resistance value being gradually variable, according to still another aspect of the present invention, comprises a resistance circuit including a plurality of resistors serially connected; and a bypass circuit connected in parallel with the resistance circuit for bypassing one or more resistors selected from the plurality of resistors, wherein the bypass circuit includes a plurality of: transistors selectively turned on or off, the plurality of transistors are connected to ends of the plurality of resistors respectively, and gate widths of the plurality of transistors are so set that the variable resistance value varies approximately in steps of a predetermined value.
In the variabe resistance circuit, the bypass circuit includes a plurality of transistors selectively turned on or off, the plurality of transistors are connected to ends of the plurality of resistors respectively. Thus, various resistance values can be set by selectively turning on or off the plurality of transistors. The gate widths of the plurality of transistors are so set that the variable resistance value varies approximately in steps of a predetermined value. Thus, linearity of the variable resistance value can be ensured. Consequently, the resistance value can be set in high precision.
A variable resistance circuit that has a variable resistance value being gradually variable, according to still another aspect of the present invention, comprises a resistance circuit including a plurality of resistors serially connected; and a switch circuit connected in parallel with the resistance circuit for bypassing one or more resistors selected from the plurality of resistors, wherein the switch circuit includes a plurality of switches selectively turned on or off, the plurality of switches are connected to ends of the plurality of resistors, and parasitic resistance values of the plurality of switches in an ON state are so set that the variable resistance value varies approximately in steps of a predetermined value.
In the variable resistance circuit, the switch circuit includes a plurality of switches selectively turned on or off, and the plurality of switches are connected to ends of the plurality of resistors. Thus, various resistance values can be set by selectively turning on or off the plurality of switches. The parasitic resistance values of the plurality of switches in an ON state are so set that the variable resistance value varies approximately in steps of a predetermined value. Thus, linearity of the variable resistance value can be ensured. Consequently, the resistance value can be set in high precision.
Each of the plurality of switches may include a CMOS switch. In this case, a circuit including the variable resistance circuit can be formed by a CMOS integrated circuit.
A variable resistance circuit that has a variable resistance value being gradually variable based on a control signal, according to still another aspect of the present invention, comprises a resistance circuit including a plurality of resistors serially connected; and a bypass circuit connected in parallel with the resistance circuit for bypassing one or more resistors selected from the plurality of resistors, wherein the bypass circuit includes a plurality of transistors selectively turned on or off based on the control signal, the variable resistance value is determined by a combined resistance value of a parasitic resistance of one or more transistors being turned on and one or more resistors being bypassed as well as a combined resistance value of one or more resistors being not bypassed, and gate widths of the plurality of transistors are so set that the variable resistance value has approximately linearity with respect to the control signal.
In the variable resistance circuit, the variable resistance value is determined by a combined resistance value of a parasitic resistance of one or more transistors being turned on and one or more resistors being bypassed as well as a combined resistance value of one or more resistors being not bypassed. Thus, various resistance values can be set by selectively turning on or off the plurality of transistors. The gate widths of the plurality of transistors are so set that the variable resistance value has approximately linearity with respect to the control signal. Thus, plurality of the variable resistance value can be ensured. Consequently, the resistance value can be set in high precision.
The plurality of transistors may be connected to ends of the plurality of resistors respectively.
A variable resistance circuit that has a variable resistance value being gradually variable based on a control signal, according to still another aspect of the present invention, comprises a resistance circuit including a plurality of resistors serially connected; and a switch circuit connected in parallel with the resistance circuit for bypassing one or more resistors selected from the plurality of resistors, wherein the switch circuit includes a plurality of transistors selectively turned on or off based on the control signal, the variable resistance value is determined by a combined resistance value of a parasitic resistance of one or more transistors being turned on and one or more resistors being bypassed as well as a combined resistance value of one or more resistors being not bypassed, and parasitic resistance values of the plurality of switches in an ON state are so set that the variable resistance value has approximately linearity with respect to the control signal.
In the variable resistance circuit, the variable resistance value is determined by a combined resistance value of a parasitic resistance of one or more transistors being turned on and one or more resistors being bypassed as well as a combined resistance value of one or more resistors being not bypassed. Thus, various resistance values can be set by selectively turning on or off the plurality of switches. The parasitic resistance values of the plurality of switches in an ON state are so set that the variable resistance value has approximately linearity with respect to the control signal. Thus, linearity of the variable resistance value can be ensured. Consequently, the resistance value can be set in high precision.
The plurality of switches may include a plurality of transistors connected to ends of the plurality of resistors respectively. Each of the plurality of switches may include a CMOS switch. In this case, a circuit including the variable resistance circuit can be formed by a CMOS integrated circuit.
A variable resistance circuit that has a variable resistance value being gradually variable based on a control signal, according to still another aspect of the present invention, comprises a resistance circuit including a plurality of resistors serially connected; and a bypass circuit connected in parallel with the resistance circuit for bypassing one or more resistors selected from the plurality of resistors, wherein the bypass circuit includes a plurality of transistors selectively turned on or off based on a control signal, the plurality of transistors are connected to ends of the plurality of resistors respectively, and gate widths of the, plurality of transistors are so set that the variable resistance value has approximately linearity with respect to the control signal.
In the variable resistance circuit, the bypass circuit includes a plurality of transistors selectively turned on or off based on a control signal, and the plurality of transistors are connected, to ends of the plurality of resistors respectively. Thus, various resistance values can be set by selectively turning on or off the plurality of transistors. The gate widths of the plurality of transistors are so set that the variable resistance value has approximately linearity with respect to the control signal. Thus, linearity of the variable resistance value can be ensured. Consequently, the resistance value can be set in high precision.
A variable resistance circuit that has a variable resistance value being gradually variable based on a control signal, according to still another aspect of the present invention, comprises a resistance circuit including a plurality of resistors serially connected; and a switch circuit connected in parallel with the resistance circuit for bypassing one or more resistors selected from the plurality of resistors, wherein the switch circuit includes a plurality of switches selectively turned on or off based on a control signal, the plurality of switches are connected to ends of the plurality of resistors respectively, and predetermined resistance values of the plurality of switches in an ON state are so set that the variable resistance value has approximately linearity with respect to the control signal.
In the variable resistance circuit, the switch circuit includes a plurality of switches selectively turned on or off based on a control signal, and the plurality of switches are connected to ends of the plurality of resistors respectively. Thus, various resistance values can be set by selectively turning on or off the plurality of switches. The predetermined resistance values of the plurality of switches in an ON state are so set that the variable resistance value has approximately linearity with respect to the control signal. Thus, linearity of the variable resistance value can be ensured. Consequently, the resistance value can be set in high precision.
Each of the plurality of switches may include a CMOS switch. In this case, a circuit including the variable resistance circuit can be formed by a CMOS integrated circuit.
An operational amplification circuit according to another aspect of the present invention comprises a variable resistance circuit and an operational amplifier, connected with the variable resistance circuit, having an amplification factor varying with the resistance value of the variable resistance circuit, while the variable resistance circuit includes a resistance circuit including a plurality of resistors serially connected; and a bypass circuit connected in parallel with the resistance circuit for bypassing one or more resistors selected from the plurality of resistors, wherein the bypass circuit includes a plurality of transistors selectively turned on or off, the plurality of transistors are connected to ends of the plurality of resistors respectively, and gate widths of the plurality of transistors are so set that the variable resistance value varies approximately in steps of a predetermined value.
In the operational amplification circuit, the aforementioned variable resistance circuit is connected with the operational amplifier for varying the amplification factor with the resistance value of the variable resistance circuit capable of varying the resistance value in high precision, whereby the amplification factor can be set in high precision.
An operational amplification circuit according to another aspect of the present invention comprises a variable resistance circuit and an operational amplifier, connected with the variable resistance circuit, having an amplification factor varying with the resistance value of the variable resistance circuit, while the variable resistance circuit includes a resistance circuit including a plurality of resistors serially connected; and a switch circuit connected in parallel with the resistance circuit for bypassing one or more resistors selected from the plurality of resistors, wherein the switch circuit includes a plurality of switches selectively turned on or off, the plurality of switches are connected to ends of the plurality of resistors, and parasitic resistance values of the plurality of switches in an ON state are so set that the variable resistance value varies approximately in steps of a predetermined value.
In the operational amplification circuit, the aforementioned variable resistance circuit is connected with the operational amplifier for varying the amplification factor with the resistance value of the variable resistance circuit capable of varying the resistance value in high precision, whereby the amplification factor can be set in high precision.
A semiconductor integrated circuit according to still another aspect of the present invention, receiving an output signal from an optical pickup, comprises an operational amplification circuit amplifying the output signal from the optical pickup and another circuit, while the operational amplification circuit and the other circuit are integrated into a single chip by a CMOS integrated circuit, the operational amplification circuit includes a variable resistance circuit and an operational amplifier, connected with the variable resistance circuit, having an amplification factor varying with the resistance value of the variable resistance circuit, the variable resistance circuit includes a resistance circuit including a plurality of resistors serially connected; and a bypass circuit connected in parallel with the resistance circuit for bypassing one or more resistors selected from the plurality of resistors, wherein the bypass circuit includes a plurality of transistors selectively turned on or off, the plurality of transistors are connected to ends of the plurality of resistors respectively, and gate widths of the plurality of transistors are so set that the variable resistance value varies approximately in steps of a predetermined value.
The semiconductor integrated circuit employs the aforementioned operational amplification circuit capable of setting the amplification factor in high precision for the amplification circuit amplifying the output signal from the optical pickup, and integrates the amplification circuit and the other circuit into a single chip by the CMOS integrated circuit, whereby a one-chip CMOS integrated circuit for an optical disk drive including a high-precision amplification circuit can be implemented.
A semiconductor integrated circuit according to still another aspect of the present invention, receiving an output signal from an optical pickup, comprises an operational amplification circuit amplifying the output signal from the optical pickup and another circuit, while the operational amplification circuit and the other circuit are integrated into a single chip by a CMOS integrated circuit, the operational amplification circuit includes a variable resistance circuit and an operational amplifier, connected with the variable resistance circuit, having an amplification factor varying with the resistance value of the variable resistance circuit, the variable resistance circuit includes a resistance circuit including a plurality of resistors serially connected; and a switch circuit connected in parallel with the resistance circuit for bypassing one or more resistors selected from the plurality of resistors, wherein the switch circuit includes a plurality of switches selectively turned on or off, the plurality of switches are connected to ends of the plurality of resistors, and parasitic resistance values of the plurality of switches in an ON state are so set that the variable resistance value varies approximately in steps of a predetermined value.
The semiconductor integrated circuit employs the aforementioned operational amplification circuit capable of setting the amplification factor in high precision for the amplification circuit amplifying the output signal from the optical pickup and integrates the amplification circuit and the other circuit into a single chip by the CMOS integrated circuit, whereby a one-chip CMOS integrated circuit for an optical disk drive including a high-precision amplification circuit can be implemented.
Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of the present invention being limited only by the terms of the appended claims.